The Red Cell Volume in a Hospital Population

INTRODUCTION The normal values for red cell volume have been widely accepted as 26 to 33 ml/kg in males and 22 to 29 ml/ ^9 in females (Dacie and Lewis 1966) and Mollison


INTRODUCTION
The normal values for red cell volume have been widely accepted as 26 to 33 ml/kg in males and 22 to 29 ml/ ^9 in females (Dacie and Lewis 1966) and Mollison (1967) quotes figures of about 30 ml/kg in males and 23.4 to 27 ml/kg in females, referring to five papers reporting investigations with radioactive iron (55Fe and 59Fe) or radioactive phosphorous (32P). Using radioactive chromium (51Cr), Retzlaff, Tauxe, Kiely and Stroebel (1969) found values which give approximately the following: in 40 "normal" males 26.8 ml/kg; in 38 normal" females 23.2 ml/kg; and in 12 "obese" females 17.3 ml/kg. The mean weight of the latter was 86.2 kg (189.6 lb.).
The present study was undertaken to determine the red cell volume in the normal subject using 51Cr. In view of the difficulties in obtaining large numbers of healthy volunteers, some patients who were willing to volunteer for the test were investigated. These were all Patients who were about to be discharged from hospital and had been up and about in the wards for at 'east seven days, and who had no clinical evidence of ar,y heart failure, bleeding or abnormality of fluid balance or active infection.

Method
The subjects were weighed without any clothing and were then asked to lie on a bed for the duration of the estimation. This was carried out essentially by the Method of Mollison and Veall (1955)  From the mean of the counts of the two 1 in 50 injection standards was subtracted the count of the supernatant standard adjusted for the haematocrit of the red cell suspension and the result divided by the mean of the counts of the two blood specimens after both had been expressed in terms of 100% red cells.
This gave the result of the red cell volume directly in litres which was then expressed as ml/kg body weight.

ACCURACY
The two 20 ml syringes (B and C) employed for injecting the red cell suspension were of glass and metal nozzle construction. They were recalibrated by making a diamond scratch on the piston and another on the barrel exactly opposite after 20 ml of distilled water had been sucked into the syringe from a watch glass with a Gillette No. 1 disposable needle fitted, the "dead space" having first been filled with distilled water. The calibrations were checked by weighing the delivered distilled water ten times, using a different Gillette No. 1 needle each time. The two ml pipettes (6 and 9) for making the 1 in 50 injection standards and the two 10 ml pipettes (S and T) used for filling the counting cup with the radioactive specimens were checked in the same way. The two 50 ml flasks (A and Z) were checked by weighing their content of distilled water after filling each flask ten times. The haematocrit tubes were of British Standard (B.S.) 2554 and were read to one tenth of a division.
The mean background count was 1.3 counts per second; that of the red cell standards was 48 c.p.s. and of the blood specimens 21 c.p.s. The radioactivity of the supernatant of the injected standards was always less than 1 % of the corresponding red cell standard.
It is concluded that the total systematic error is unlikely to exceed 1% and that the random error due to counting is about the same magnitude.

RESULTS
The results of the red cell volume estimate together with packed cell volume, weight, age and description of the subjects tested are given in Tables 1 to 7. Table 7 is a summary of all the other tables.   Table 3 Table 4 Summary

DISCUSSION
It will be noted that the results differ little from those accepted as normal and quoted by Dacie and Lewis (1966). The expected significant difference was found between the results of the male and female volunteers and between those of all males and all females. The reason for the lack of significance be-tween the hospital males and the hospital females is not clear. There were of course only a relatively few hospital females and the mean red cell volume of the hospital males was rather lower than the normal volunteer males and also rather below the accepted normal range for males. Obesity did not appear to be a particular factor in lowering the red cell volume (expressed as ml/kg). Every care has been taken in this series of estimations to keep both the systematic error and the error in radioactive counting down to a low level. Repeat tests were not done on the same subject purposely to avoid any unnecessary radioactive exposure though it Would have been possible in the circumstances to check the "repeatability" of the estimation in mathematical terms.